Conventionally, a belt transmitting mechanism has been used as a means for reducing the rotational speed of a crank shaft of an internal combustion engine as a drive source and transmitting the reduced rotation to an auxiliary apparatus such as a water pump or cooling compressor as a driven source. Such a belt transmitting mechanism is composed of a drive pulley having a small diameter, a driven pulley having a large diameter, and a belt wound around these pulleys. The rotation of the crank shaft is reduced from the drive pulley through the belt to the driven pulley, and is transmitted to the auxiliary apparatus.
However, recently, the internal combustion engine has been provided with a supercharger to obtain a high output so that it is sometimes necessary to rotate the crankshaft at a speed higher than the one in the conventional apparatus. In this case, the rotation of the crankshaft is transmitted to an auxiliary apparatus without sufficiently reducing the high speed rotation of the crankshaft by a conventional belt transmitting mechanism. Therefore, the auxiliary apparatus is rotated at a high speed higher than a predetermined speed so that high heat is generated in frictional elements in the auxiliary apparatus, thereby damaging the auxiliary apparatus.
It is possible to greatly reduce the rotational speed of the crankshaft and transmit the rotation thereof by increasing the pulley ratio of the belt transmitting mechanism. To increase the pulley ratio, it is necessary to reduce the diameter of the drive pulley since it is not possible to increase the size of the driven pulley in an engine room having a small space to be utilized. However, the belt wound around the drive pulley has a limited radius of curvature so that the drive pulley cannot be set to have a diameter less than a predetermined diameter, and the speed reduction by the belt transmitting mechanism is limited.
Further, the auxiliary apparatus is excessively rotated at a high speed by the internal combustion engine through the crankshaft, thereby increasing the fuel cost.
When the rotational speed of the internal combustion engine is greatly reduced to transmit the rotational force thereof to the auxiliary apparatus, although the auxiliary apparatus is desirably rotated at a rotational speed higher than a predetermined rotational speed at the low rotational speed of the internal combustion engine, the rotational speed of the auxiliary apparatus is greatly reduced and the auxiliary apparatus is rotated at a rotational speed less than the predetermined rotational speed. Accordingly, it is not possible to sufficiently fulfill the function of the auxiliary apparatus.
In another conventional auxiliary drive apparatus of an internal combustion engine, the rotational speed of the crankshaft of the internal combustion engine is steplessly changed by a stepless speed change mechanism, and the rotation thereof is transmitted to a pulley for driving the auxiliary apparatus.
However, in such an internal combustion engine, a massive auxiliary apparatus is attached to the crankshaft in place of a single pulley having a small mass so that the tortional oscillation of the crankshaft tends to be amplified.
In such an auxiliary apparatus of the internal combustion engine, there is no means for reducing the tortional oscillation of the crankshaft so that a noise due to the tortional oscillation is generated and the crankshaft might be damaged by the fatigue thereof in some cases, and a crank bolt for attaching the auxiliary drive apparatus to the crankshaft might be untightened.
In a conventional automobile for example, it is not necessary to rotate an auxiliary apparatus such as a power pump, air compressor, alternator, etc., at a speed higher than a predetermined speed. Further in some cases, it is preferable that the auxiliary apparatus is not rotated at a speed higher than the predetermined speed even when the number of rotations of the internal combustion engine is increased. Accordingly, recently the rotational force of the internal combustion engine has tended to be transmitted to the auxiliary apparatus through an automatic speed change device.
However, it is important from the view point of the engine cooling that a water pump among respective auxiliary apparatuses is rotated in proportion to the increase of the number of rotations of the internal combustion engine. However, in such a conventional apparatus, two rotary forces different in nature from each other cannot be obtained from a single speed change device so that it is necessary to dispose another means transmitting the rotary force and directly connected to a rotary shaft of the internal combustion engine in addition to the speed change device.
Accordingly, the size of the auxiliary drive apparatus is increased, and the structure thereof is complicated.